MEMS components and devices can be integrated with micro systems that combine electrical and mechanical components. MEMS devices can be fabricated utilizing standard integrated circuit batch processing techniques and are capable of being utilized for a variety of applications such as, for example, sensing, controlling, and actuation on a micro scale. MEMS devices can function individually or in the context of, for example, arrays, in order to generate particular effects on a macro scale.
Many MEMS devices require a vacuum environment in order to attain maximum performance and to provide a high vacuum for enhanced performance and reliability. Such a vacuum package also provides protection and an optimal operating environment for the MEMS device. For generating a high vacuum that is free from hydrocarbons, several types of turbomolecular vacuum pumps are known. Through the use of such vacuum pumps pressures in the molecular pressure range (e.g., approximately between 10-6 torr and higher) vacuum levels in macro-scale systems can be achieved. Maintaining such a vacuum at the chip-scale level, however, offers unique challenges due to scaling laws and practical limitations. The large surface-to-volume ratio and relatively large sealing perimeters, out-gassing, permeation, and diffusive leakage, present greater difficulties for chip-scale vacuum pumping applications.
Typical chip-scale MEMS devices that use silicon and metal surfaces can adsorb or entrap volatile molecules from ambient exposure and processing (e.g. plasma, CVD). Therefore, high temperature bake out procedure is needed to remove (out-gas) volatile molecules and residual contaminants, otherwise out-gassing occurs slowly over a long time or even throughout the operating life of the device, acting as a virtual leak. Most prior art MEMS and electronic devices cannot be subjected to a post-processing high temperature bake out (>300° C.) and are unable to form high temperature metallurgical sealing (e.g., welding or brazing). Consequently, both virtual and real leaks are expected to be present throughout their operating life making it difficult to develop viable vacuum packaged MEMS devices.
Based on the foregoing, it is believed that a need exists for an improved chip-scale vacuum pump offering sufficient pump speed to evacuate the volume gas quickly and to counter the out-gassing and leakages from all sources at the targeted low pressure. A need also exists for an improved radial turbomolecular pump with an electrostatically levitated rotor, as described in greater detail herein.